Supported Ruthenium as Alkyne Semy-Hydrogenation Catalyst

C.R. LEDERHOS; P.C. L'ARGENTIÈRE; F. COLOMA-PASCUAL; N.S. FÍGOLI

Costa Verde, Brasil

Congreso; 2nd Mercosur Congress on Chemical Engineering. 4th Mercosur Congress on Process Systems Engineering; 2005

Ruthenium (5%) on alumina was prepared by the incipient wetness impregnation technique using ruthenium chloride as precursor and reduced at two temperatures: 373 or 573 K. The catalytic behavior during the selective hydrogenation of 1-heptyne to 1-heptene was studied at 303 K, 750 rpm and at a hydrogen pressure of 150 KPa in a stirred tank reactor. The solids were characterized by X-ray Photoelectron Spectroscopy. The results show that the reduction temperature influences the electronic state of ruthenium. At both reduction temperatures Ru° as well as electron-deficient Run+ species exist. At the lowest reduction temperature, more electron deficient Ru species are present. The total conversion, as well as the selectivity and the conversion to 1-heptene were higher at the higher reduction temperature. The higher conversion may be attributed to the fact that ruthenium is more electron-deficient at 373 K. The Run+ species, having less available electrons, could not interact so strongly with the alkyne molecules as Ru°, thus decreasing activity. The alkyne molecules are more strongly adsorbed on the catalyst reduced at 573 K than on the catalyst reduced at 373 K because there are more Ru° species. Also, the alkyne is much more strongly adsorbed than the alkene: there exists a competitive adsorption between both species. Due to the preferential adsorption of the alkyne, the alkene, once formed, is easily desorbed; hence its further over hydrogenation is decreased thus increasing selectivity. Because of the strongest alkyne adsorption at 573 K, the selectivity of this catalyst is higher. The Ru/Al2O3 catalyst reduced at 573K was compared with the classic Lindlar catalyst (Pd/CaCO3 modified with Pb(OAc)2). In the operational conditions of this work Ru/Al2O3 is less active but more selective than the commercial catalyst. Ru/Al2O3 also has the advantage to be a pelletized material.